The present invention relates to an IC (Integrated Circuit) card, and more particularly to an IC card from which internal data including secret data cannot be illegally read.
Recent years have been called "the cashless era." Many things can be bought by using personal identification (ID) cards issued by credit companies and the like, eliminating the need to pay in cash.
Various kinds of ID cards are available at present, such as plastic cards, embossed cards, and cards with a magnetic stripe. From a structural point of view, these cards are easy to forge. Further, the data recorded on them can be easily read. Many cases of their illegal use have been reported, and this has become a great social problem.
To resolve this problem, IC cards with a built-in CPU and a built-in IC memory have been developed. The IC memory stores various data about the card owner, such as his or her personal identification number. The data cannot be easily read from the IC memory. Recently, an IC card system comprising such IC cards and terminals has been put to practical use.
FIG. 1 is a perspective view of an IC card. As shown in this figure, eight connection pads 12 are arranged on plastic card body 10, in two vertical rows, each consisting of four pads. When the IC card is inserted in a terminal, connection pads 12 contact the corresponding pins provided in the terminal, thereby electrically connecting the IC card to the terminal. Of these eight pads, only six are actually used at present. Magnetic stripe 14 is adhered to the surface of card body 10.
An integrated circuit (IC) of the structure shown in FIG. 2 is formed within card body 10. This IC comprises CPU (Central Processing Unit) 20 and EEP-ROM (Electrically Erasable Programmable--Read Only Memory) 22. The six connection pads, i.e., input/output terminal I/O, clock terminal CLOCK, reset terminal RESET, power supply terminal Vcc, ground terminal GND and data-writing power supply terminal Vpp, are provided in the IC. Due to its specific use, the IC must be greatly reliable. Therefore, it is subjected to an extremely strict test before delivery. EEP-ROM 22 is tested by inputting data to it, and outputting data from it, through input/output terminal I/O, bit by bit. Obviously, this method of testing EEP-ROM 22 requires too long a time. To save time, data pads D1 to Dn are coupled to n-bit data bus 24 connecting CPU 20 and EEP-ROM 22, and address pads A1 to Am are coupled to m-bit address bus 26 connecting CPU 20 and EEP-ROM 22. The test probe designed to test EEP-ROM 22 is put into contact with data pads D1 to Dn and address pads A1 to Am, whereby EEP-ROM 22 can be tested within a short time.
After EEP-ROM 22 has been tested, leads 30 are bonded to eight pads 12 as illustrated in FIG. 3, but no process is performed on data pads D1 to Dn or address pads A1 to Am. Thereafter, the IC is incorporated into card body 10. More precisely, IC pellet 32 containing the IC (FIG. 2) is put within recess 34a made in base plate 34 of card body 10, and is then so positioned to have eight pads 12 aligned with leads 30, respectively. Leads 30 are then bonded to pads 12.
If the IC card happens to fall into the hands of a person other than the card owner, either by theft or loss, and the IC is removed from card body 10, the data including secret data stored in EEP-ROM 22 can be read merely by touching a test probe to data pads D1 to Dn and address pads A1 to Am, which remain intact. In other words, the IC card can be forged based on the data thus read from EEP-ROM 22. This greatly reduces the security of the IC card. In the worst possible case, the technical aspects of the IC card system as a whole can be analyzed and unlawfully utilized on a large scale.